Expansion against cement for zonal isolation

ABSTRACT

A method for improving zonal isolation between formations along a borehole, comprises a) providing a pipe in the borehole, wherein at least a portion of the pipe lies between the formations, b) providing a body of cement in the annulus between the borehole wall and said pipe portion, c) allowing the body of cement to cure until it has reached at least 70 Bearden units consistency, and d) expanding said pipe portion so as to decrease the cross-sectional area of the annulus between the borehole wall and said pipe portion.

RELATED CASES

This application claims benefit of U.S. Application Ser. No. 61/165,128,filed on Mar. 31, 2009, which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to the use of cementitious materials outside of adownhole tubular as a means for providing zonal isolation afterexpansion of a tubular.

BACKGROUND OF THE INVENTION

In the context of oil and gas drilling, cementitious materials,including but not limited to Portland cements, resins, blast-furnaceslag, and blends of those materials, are typically placed in the annulusbetween the casing and the wellbore so as to isolate and protect thecasing during drilling, completion, and operation of the well. Oncepumped in place and allowed to harden, these materials provide isolationbetween the various formations and between the formations and surfacesuch that the hydrocarbons can be safely produced, or alternatively thewellbore can be used for injection operations.

After cement has hardened in a wellbore, it is well known that thehardened cement may not fill the annuls as completely as desired. Inaddition the hardened cement may be subjected to mechanicaldamage—stress fractures and/or separation from the casing wall(debonding)—such that hydraulic isolation may be jeopardized. Likewise,during the process of expanding tubulars that are surrounded by hardenedcement, mechanical failure of the cement may cause zonal isolation islost. Thus, it is desirable to provide a system by which a tubular canbe expanded in a wellbore and still maintain annular hydraulicisolation.

Drilling operations that include the use of expandable tubulars arebecoming more common. Expansion can be carried out using a top-downtechnique, in which an expansion tool starts at the upper end of theexpandable tubular and is pushed through the tubular until it hasexpanded the full length of the tubular, or using a bottom-up technique,in which an expansion tool starts at the bottom of the tubular and ispulled upward through the tubular. Regardless of which technique isused, if the tubular is not anchored, it will move with the expansiontool. Without movement of the expansion tool relative to the tubular,expansion will not occur.

In top-down expansion techniques, the downward force of the expansiontool on the tubular can be resisted by anchoring the tubular to anadjacent tubing string or applying an upwards force by some other means.In bottom-up expansion, however, it is typically desirable to leave thetop end of the tubular free to move within the borehole, so as to allowfor the axial shrinkage of the tubular will occur during expansion.Therefore, it may not be practical to use top-anchoring techniques andit may be desirable to anchor the lower end of the tubing instead.

One way to perform a bottom-up expansion is to use a mechanical jack.The mechanical jack works within the tubular and expands a section ofthe tubular without requiring additional outside forces to be applied tothe tubular. The localized expansion serves to anchor the tubular stringin the wellbore sufficiently that the expansion tool can then be pulledthrough the tubular. Thus, a jack can be used to expand and anchor thelower end of a tubular for a bottom-up expansion. Anotherwell-established method for expanding tubulars in a wellbore uses onlyhydraulic pressure.

Despite the state of the art, it remains desirable to provide a meansfor achieving zonal isolation in situations where it is not practical toaccess the annulus.

SUMMARY OF THE INVENTION

In accordance with preferred embodiments of the invention, means areprovided for means for achieving or improving zonal isolation insituations where it is not practical to access the annulus, such as whencement has already hardened in the annulus.

In certain embodiments of the invention zonal isolation betweenformations along a borehole is improved by a) providing a pipe in theborehole, wherein at least a portion of the pipe lies between theformations, b) providing a body of cement in the annulus between theborehole wall and said pipe portion, c) allowing the body of cement tocure until it has reached at least 70 Bearden units consistency, and d)expanding said pipe portion so as to decrease the cross-sectional areaof the annulus between the borehole wall and said pipe portion.

Step d) may eliminate fluid channels in the cement body and/or increasethe density of the cement body. Step c) may or may not cause the secondcement body to fracture. The method may further include providing asecond cement body in the annulus, wherein the second cement body has alonger cure time than the first cement portion. The second cement bodyis not necessarily cured when step d) is carried out.

At least one of the cement bodies may contain ringing gels and/or otherpolymers.

The method may further include the step of providing an exit path forwater expelled from the cement during expansion.

In some embodiments, the hardened cement material is designed to havespecific mechanical properties such that it can withstand sufficientforces to allow the tubular to be radially expanded to a largerdiameter. Some embodiments of the invention include a two-slurryapproach in which a relatively rapid-hardening cement slurry is placedin the annulus around the lower portion of the tubular to be expanded,and a second, slower-setting slurry is placed around a second portion ofthe tubular and does not harden until after the expansion process iscomplete.

In other embodiments, one or both cement slurries are designed to havemechanical properties such that the slurry placed around the bottom ofthe tubular provides the means to anchor the tubular during initiationof expansion, but without resulting in mechanical failure of one or bothcement sheaths. In further embodiments, either cement slurry may containelastomeric materials that swell if contacted by wellbore orsubterranean fluids such as water, hydrocarbon, gas, and/or drillingfluids, etc., and re-establish annular hydraulic isolation, even if thepresence of mechanical damage to the hardened cement.

As used in this specification and claims the following terms shall havethe following meanings:

The word “anchor” refers to a system or device that provides sufficientengagement between the tubular and the borehole wall to allow anexpansion tool to move relative to the tubular and thus to expand thetubular.

As used herein, “liner” and “casing” are used interchangeably, inasmuchas aspects of the invention that relate to casings also relate toliners, and vice versa.

Unless otherwise indicates, as used herein the terms “bottom,” “lower,”and “downhole” refer to locations that are farther from the surface,even if the borehole is not vertical.

It is further understood that said cement formulations may contain anyadditives that are known in the art to achieve specific slurryproperties necessary for pumping and placement, including additives andgases for foamed cements.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed understanding of the invention, reference is made tothe accompanying wherein:

FIG. 1 is a schematic illustration of the bottom of a borehole in whichan expandable liner and a tubing string are present.

FIG. 2 is a schematic cross-section along lines 2-2 of FIG. 1.

FIG. 3 is a schematic cross-section showing the system of FIG. 2post-expansion.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring initially to FIGS. 1 and 2, a borehole 10 may contain anexpandable liner 12 and a tubing string 14. An expansion device 16 isaffixed to the lower end of the tubing 14. Expansion device 16 isillustrated as an expansion cone, but may be any suitable device that iscapable of incrementally radially expanding the expandable liner as thedevice moves through the casing. This assembly may further include aneccentric guide nose, stabilizer above the cone, autofill float collar,a dart catcher, two darts, safety joint, debris catcher and drill pipeto surface (all not shown), such as are known in the art. The equipmentis made up and lowered into the hole with the drill pipe.

If the upper end of liner 12 (not shown) is free to move within theborehole, then upward force applied to expansion device 16 will merelymove liner 12 upward and will not result in expansion. In order toprovide the requisite movement of expansion device 16 relative to liner12, it is necessary to anchor liner 12 in the borehole.

If the requisite anchoring of the tubular is not accomplished bymechanical means at the upper end of the liner, such as an engagementwith the lower end of the adjacent upper tubular, or by mechanical meansat the lower end of the liner, such as by use of a jack, then theanchoring may be provided by the cement. In the discussion below,discussions of cement refer to cement in the annulus between liner 12and borehole 10 as shown at reference numeral 18. Specifically, thecement may provide a mechanical engagement between the outside of thetubular and the inside of the borehole wall. If the cement is the soleanchoring means, the mechanical engagement must be sufficient torestrain the tubular against the strong upward force that is applied atthe initiation of expansion. Apart from or in addition to being used asan anchoring means, cement is also typically used to seal the annulus.

In preferred embodiments, the cement is mixed and pumped downhole. It ispreferably separated from the other fluids by the two darts as it ispumped. The first dart lands in the dart catcher, indicating that thecement is about to enter the annulus. Extra fluid is pumped until thesecond dart lands, indicating that all the cement is in the annulus.Pumping is preferably stopped after a few barrels are pumped to clearthe drill string of any cement. Once the pumping stops, the float collaracts as a back pressure valve to prevent the cement from flowing back upthe drill string. After a predetermined amount of time to allow thecement to at least partially cure, casing expansion is initiated bypulling on the drill string to start movement at the cone. The safetyjoint is preferably included in the assembly to enable easy release fromthe drill string if there are any problems with the tools or operations.

It has been discovered that it is possible to improve zonal isolation inan area that has been cemented, by expanding a tubular against thecement, as shown in FIG. 3. If the cement is crushed, it may increase indensity, closing channels or pockets that might otherwise allow fluidflow in the annulus. Thus, if the cement can be expanded so as todecrease its cross-sectional area, i.e. by decreasing the area of theannulus, defects in the cement may be eliminated and a superior sealformed in the annulus.

It has further been discovered that cement that has been allowed to atleast partially cure before expansion may provide a superior annularseal after expansion. Thus, in preferred embodiments, the cement isallowed to hydrate to a point at which its pumpability is at least 70Bearden units of consistency (Bc). Once the cement has cured to thispoint, an expansion device is advanced through the liner, therebycausing a radially outward expansion of the liner. If the formation issufficiently resistant to compaction, radial expansion of the liner willcause a reduction of the cross-sectional area of the annulus,pulverizing and compacting the cement.

Because the expansion pulverizes the cement, any channels or pocketsthat may have initially been present in the annulus cement areeliminated and zonal isolation in the expanded region is improved. Thus,the present invention can be used to cure defective cement seals, whichmay be located by logging or indicated by the presence of fluid flow inthe annulus.

Some embodiments of the invention include a two-slurry approach in whicha more-rapidly-setting cement slurry is placed in the annulus around afirst portion of the tubular to be expanded, thereby providing anoptional anchor, and a second, slower-setting slurry is placed around asecond portion of the tubular and does not harden until after theexpansion process is complete, so that formation isolation is enhanced.The second slurry may be provided above the first in the annulus, asshown at 22 in the Figure, or below it. In these embodiments, thefaster-setting cement portion may be fractured during the expansionprocess but may nonetheless retain its ability to anchor the tubular.

In embodiment where both fast- and slow-setting cements are used, thecure time for each cement portion will depend on various factors,including downhole temperature, cement water content, and the presenceof additives. It is preferred that these factors be controlled, to theextent possible, such that the fast-setting cement portion sets within afirst pre-determined time window and the slow-setting cement portionsets within a second pre-determined time window that is longer than thefirst pre-determined time window. By way of example only, the firstcement may cure in less than 12 hours, while the slow cement may cure inno less than 50 hours.

In other embodiments, one of the cement slurries may be designed to havemechanical properties such that the slurry placed around the bottom ofthe tubular provides the means to anchor the tubular during initiationof expansion, but can be radially expanded without resulting inmechanical failure of one or both cement sheaths. The formation of acement layer that can be radially expanded without fracturing can beaccomplished by use of various blends of latexes, rubber particles,fibers, and binders that cure in place, such as hydraulic cements,cross-linked polymers, resins, rubber, and the like.

The parameters that preferably controlled in this embodiment include theshear bond between the pipe and the cement, and the mechanicalproperties of the cement itself, including its Young's Modulus, Poissonratio, cohesion, and friction angle. Methods for determining desiredranges for these properties and for controlling them in the cement areknown to those of skill in the art.

In certain embodiments, the cement portion that is used to anchor theexpandable liner can include a crosslinked polymer gel, including thoseknown in the art as ringing gels. Examples of suitable polymers includethose disclosed in U.S. Pat. No. 7,267,174. In preferred embodiments,the cement portion that anchors the expandable liner comprises across-linked polymer and a suitable cementitious material, including butnot limited to Portland cement, pozzolan, and/or slag.

In some embodiments, the cement does not fully cure before expansionoccurs, so the cement portion that functions as an anchor is onlypartially cured. In such cases, it is preferred to calculate the minimumlength of tubing that must be cemented, using parameters such as thoseset out above. A cement that provides a high shear bond to the pipe mayrequire only a relatively short length of cemented pipe for to providethe anchoring force, while a cement that does not achieve as much shearbond at the time of expansion will require contact with more of thesurface area of the tubular and thus a greater axial portion of theannulus.

The following Example illustrates some of the foregoing concepts.

Example 1

A 9⅝-inch, 43.5 lb/ft casing section 24-inches long was placed inside anouter jacket of 13⅜-inch casing. Before installation, the outside of the9⅝-inch pipe was blasted with medium grit aluminum oxide to increase theroughness of the pipe, thus improved shear bond between the pipe and thecement. The annular gap was filled with a cement slurry composed of APIClass H Portland cement+73% fresh water+0.6% Hydroxyethyl cellulose(viscosifier)+0.2% fluid loss agent, mixed at 13.8 lb/gal. The cementwas cured at 170° F. and atmospheric pressure for approximately 8 hrs,at which time samples indicated a compressive strength of 579 psi. Atthis time a force was applied to the 9⅝-inch casing while holding theouter jacket and cement stationary. The force required to break theshear bond between the cement sheath and the 9⅝-inch casing was recordedas 38,200 lbs, which equates to 68.2 psi. This information is then usedto determine the length of cemented casing required to act as the anchorto perform the expansion. For example, 100 ft of cemented casing wouldbe expected to withstand 2.4 millions lbs of tensile force.

It is understood that anchor slurries in accordance with the presentinvention can be composed of any Portland or non-Portland cementitiousmaterial, and likewise make use of any mixing fluids and additives thatare known in the art to provide a pumpable slurry that can be placed inthe wellbore as desired. Further, it is also understood that thecomposition may contain any additive or combination thereof as is knownin the art to achieve specific mechanical properties such as but notlimited to elastomers, polymers, copolymers, latexes, binding agents,fibers, salts, and aggregates. Examples of suitable polymers include thePermSeal® and H₂Zero® products available from Halliburton, Houston, Tex.

In still further embodiments, either cement slurry may containelastomeric materials that swell if contacted by wellbore orsubterranean fluids (water, hydrocarbon, gas, and/or drilling fluids,etc.) and re-establish annular hydraulic isolation, even in the presenceof mechanical damage to the hardened cement. Such swellable elastomersare known to those skilled in the art.

Regardless of which cement properties are selected for implementation ofthe present invention, it may also be desired to increase the shear bondof the cement to the pipe so that it is less likely to separate from thesurface of the tubular in the presence of shear forces. Techniques forachieving this are well known in the art and include but are not limitedto the addition of post-set expanding agents (manganese oxide,tricalcium aluminate, salts) to the cement slurry, plastic set expanders(foam, reactive gas generators), and surfactants.

Expelled Water

It has further been discovered that when an expansion device is pulledthrough a portion of a tubular that is anchored in cured cement, thecompression force applied to the cement is great enough to forceunreacted water out of the cured cement. As is known by those skilled inthe art, most hydraulic cements use only a portion of the water presentto react, and the remainder of that water is present only to aid inmixing and placing the slurry. The amount of water expelled from thecement during the expansion process may be significant. If no escapepath is provided, this trapped water may result in challenges such asexcessive force required to perform the expansion, even beyond thecapabilities of the drilling rig, or a pressure increase sufficient todamage the pipe, even to the point of collapse. It is recognized thatsome portion of, and in some cases all, of this unreacted water mayescape to the formation via either natural permeability, or natural orinduced fractures. However, this outlet may not always exist or bepresent in such a volumetric flow rate to accommodate the desiredexpansion rate. It is believed that significant advantages may berealized by providing a pathway by which such expelled water can escapefrom the compression zone.

One way to provide a pathway for the expelled water is to provide anin-place sacrificial collapse volume in the cement sheath. With thismethod, as the expansion occurs and the annular gap between the casingand formation or between casings is reduced, the sacrificial collapsevolume provides an in situ compressible volume, thus a means to preventtrapped pressure build up during the expansion process. One method toprovide this collapsible volume to the cement sheath are foamed cement,in which the cement is foamed with a gas such as air or nitrogen duringpumping so that after it hardens the cement sheath includes a volumefraction of compressible gas. Another means of providing for in situcollapse can be achieved by including hollow microspheres in the cementblend such, as the borosilicate hollow microspheres available fromcompanies such as 3M Corporation. It will be obvious to one skilled inthe art that either of these methods also reduces the volume ofunreacted water per volume of set cement, and that the sacrificialcollapse volumes can be customized on a well-by-well basis. Further, itwill be obvious that the collapsible cement sheath may also includeother mechanical modifiers such as but not limited to thepreviously-mentioned rubber particles, copolymers, latex, insitu gasgenerating compounds, and other means.

Other means to provide a pathway for hydraulic relief to the annular gapbehind the expandable tubular include but are not limited to shunttubes, rupture disks, volume chambers, and the like that will beapparent to one skilled in the art.

In one preferred embodiment, it may be desirable to prepare the wellborein such a way to initiate volume relief. This may be accomplished byseveral means, including but not limited to exerting hydraulic pressurein the wellbore prior to expansion to initiate wellbore failure. Inanother embodiment, the formation may be affected by creating stressrisers via hydrojetting the formation prior to running the expandabletubular in the wellbore. This would create a weakness in the formationand allow it to more easily fail due to pressure buildup during theexpansion process, but not necessarily fail prior to that point and thusallowing the wellbore to be more easily controlled, circulated, andcemented.

In some preferred embodiments, the cement in the annulus isoverdisplaced, so that the lower end of the expandable tubular issurrounded by drilling fluid, cement spacer, or other noncementitiousfluid at the bottom of the hole. Further, this fluid may also consist ofa hydraulic cement that has a longer set time that the anchoring cementabove it. This process is preferred so as to allow the initiation of theexpansion process to occur with less force.

In some preferred embodiments, it may be desired to pump an additionalhydraulic cement or other fluid after the expansion process has beencompleted. The purpose of this fluid would be to ensure that therubblized cement in the annulus of the expanded tubular does not leak orotherwise allow communication of fluids behind the expanded tubular fromdeeper formations. This practice is commonly referred to by thoseskilled in the art as a shoe squeeze.

It will be understood that the cement anchoring techniques disclosedherein can be used alone, or in combination with other anchoringtechniques, such as jacks or hangers. Likewise, the techniques disclosedherein can be repeated for successive lengths of expandable liner, andeach length may be expanded to the same inside diameter, so that amonodiameter borehole is formed.

1. Method for improving zonal isolation between formations along aborehole, comprising: a) providing a pipe in the borehole, wherein atleast a portion of the pipe lies between the formations; b) providing abody of cement in the annulus between the borehole wall and said pipeportion; c) allowing the body of cement to cure until it has reached atleast 70 Bearden units consistency; and d) expanding said pipe portionso as to decrease the cross-sectional area of the annulus between theborehole wall and said pipe portion.
 2. The method of claim 1 whereinstep d) eliminates fluid channels in the cement body.
 3. The method ofclaim 1 wherein step d) increases the density of the cement body.
 4. Themethod of claim 1, further including the step of providing a secondcement body in the annulus, wherein the second cement body has a longercure time than the first cement portion.
 5. The method of claim 4wherein the second cement body is not cured when step d) is carried out.6. The method of claim 4 wherein at least one cement body containspolymers.
 7. The method of claim 6 wherein at least one cement bodycontains ringing gels.
 8. The method of claim 4 wherein step c) does notcause the second cement body to fracture.
 9. The method of claim 1,further including the step of providing an exit path for water expelledfrom the cement during expansion.